1. Field of the Invention
The present invention relates primarily to a thin-film magnetic head comprising an induction type magnetic transducer device for recording purposes, and a thin-film magnetic recording head comprising a magneto-resistive effect device adapted to read the magnetic field intensity of a magnetic recording medium or the like in the form of signals.
2. Explanation of the Prior Art
In recent years, for instance, magnetic recording mediums such as hard disks (hereinafter called simply the “recording medium or mediums”) have grown in surface recording densities and, with this, there is a growing demand for improvements in the performance of a thin-film magnetic recording head mounted on a magnetic recording system such as a hard disk drive.
As well known in the art, for instance, such a thin-film magnetic recording head operates in two recording modes: a longitudinal recording mode where the direction of a signal magnetic field is set in the planar (longitudinal) direction of a recording medium, and a perpendicular recording mode where the direction of a signal magnetic field is set perpendicularly to the surface of the magnetic recording medium.
Although the longitudinal recording mode is now used in common, yet the perpendicular recording mode is promisingly expected to supercede the longitudinal recording mode, in consideration of future market trends in association with improvements in the surface recording densities of recording mediums. The perpendicular recording mode has the advantages of just only ensuring high recording densities but also making the recording medium with information already recorded in it less vulnerable to thermal fluctuations.
A thin-film recording head of the perpendicular recording mode is constructed typically of a thin-film coil adapted to generate a recording magnetic flux, and a main magnetic pole layer that extends from an air bearing surface toward the rear and is adapted to generate a magnetic field (perpendicular magnetic field) for magnetizing a recording medium on the basis of the recording magnetic flux generated at the thin-film coil. With such a thin-film head of the perpendicular recording mode, the recording medium is magnetized on the basis of the perpendicular magnetic field generated at the main magnetic pole layer, so that information can be magnetically recorded in that recording medium.
For such a thin-film magnetic head of the perpendicular recording mode, for instance, a thin-film magnetic head comprising a main magnetic pole layer located in such a way as to extend in a direction orthogonal to an air bearing surface is known. Such a type of thin-film magnetic head of the perpendicular recording mode is generally called a “single-pole type thin film magnetic head”.
Referring here to a specific structure of that single-pole type thin-film magnetic head known so far in the art, for instance, an auxiliar magnetic pole layer for seizure of an auxiliar magnetic flux is joined to the main magnetic pole layer to enhance the intensity of a perpendicular magnetic field, thereby improving on overwrite capability (see, for instance, JP(A)'s 02-066710, 2002-197615 and 2001-250204, and EU(A)0360978).
As far as the improvement in overwrite capability is concerned, however, there would appear to be some limit to the single-pole type thin-film magnetic head.
In a thin-film magnetic head of the perpendicular recording mode recently proposed in the art, a main magnetic pole layer that extends in a direction orthogonal to an air bearing surface as described above is combined with a write shield layer adapted to hold back the spread of a magnetic flux emitted out of that main magnetic pole layer, so that the recording track width is prevented from becoming wide thereby increasing the recording density of a recording medium.
Such a thin-film magnetic head of the perpendicular recording mode is generally called a “shield type thin-film magnetic head”. The write shield layer is spaced from the main magnetic pole with a gap of up to 0.2 μm between them, and extends from the air bearing surface toward the rear, whereby it is isolated by a gap layer from the main magnetic pole layer on a side near to the air bearing surface and joined through a back gap to the main magnetic pole layer on a side far away from the air bearing surface.
With the write shield type thin-film magnetic head comprising such a write shield layer, the recording density of the recording medium is improved, because there is a sharp gradient to the perpendicular magnetic field by virtue of restrictions on the spread of a magnetic flux emitted out of the main magnetic pole layer.
Here, to better the reliability of the thin-film magnetic head of the perpendicular recording mode, regardless of whether it is of the type having the so-called shield (the shield type thin-film magnetic head) or of the type having an auxiliar magnetic pole, it is necessary to get stable hold of magnetic operation performance. Problems with the prior art thin-film magnetic head are, however, that as unwanted magnetic fields (floating external magnetic fields) arise from an external magnetic field source such as a voice coil motor, it causes unintended write (overwrite) during non-recording, that is, during no supply of recording currents to a thin-film coil, although depending on the influences of such floating external magnetic fields, and this often results in inadvertent erasure of information recorded in a recording medium. To get stable hold of the magnetic operation performance of the thin-film magnetic head of the perpendicular recording mode, there is thus now a growing demand for the technique of holding back inadvertent erasure of information as much as possible at the time of non-recording.
With the prior art shield type thin-film magnetic head, besides, there is a PTP (pole tip protrusion) phenomenon stemming from the generation of heat from coils or external temperature changes, i.e., a phenomenon wherein the pole tip protrudes from the ABS surface, because the shield member itself is a large magnetic material. Reducing the thickness of the shield member itself may work for prevention of the PTP; however, the thickness reduction conversely gives rise to the tendency of the above external magnetic field resistance to become worse. Thus, both have tradeoff relations.
Such being the prior art situation, an object of the invention is to provide a thin-film magnetic head structure that is improved in terms of the so-called external magnetic field resistance, and is capable of just only preventing inadvertent erasure of information recorded in a recording medium as much as possible, but also holding back the PTP (pole tip protrusion) phenomenon arising from the generation of heat from coils or external temperature changes.
For a combination of upper and lower magnetic shield layers located above and below a read-only magneto-resistive effect device with it held between them so as to have a magnetic shield action on it, too, there is the same demand, because there are often similar problems with the above write-only thin-film magnetic head.